During the age of dinosaurs, life did not end when the sun went down. In fact, it only became more dangerous.
Paleontologists have long believed that dinosaurs were mostly active during the daytime. This conjecture was based on the assumption that dinosaurs were cold-blooded and that their internal body temperature was regulated by the environment.
Scientists argued that nights were too cold during the Mesozoic era for dinosaurs to be active. However, a new study by the University of California, Davis challenges this assumption and offers new insight into the lives of dinosaurs.
Scientists studied the structure of sclera rings, a series of bony plates which support the sclera region of the eye socket, of modern animals and compared them to that of dinosaurs.
According to the study, which was published in Science magazine, researchers examined the sclera ring of over 160 species alive today and then compared their findings to 33 species of dinosaurs that lived throughout the Mesozoic era, which spanned from 250 million to 65 million years ago. They found that there are similarities in the sclera ring size between modern animals and dinosaurs. Through the comparison, subtle differences in size were correlated with sleeping behaviors.
The study found that nocturnal species had relatively large scelera rings, potentially to allow more light to enter for the night roamers. Species active in the day, which have much more light with which to see, had smaller scelera rings. The smaller openings reduced how much the dinosaurs had to restrict their pupils and also allowed them to see a clear and focused image at a large range of depth.
In addition, species active during both the day and night had midsized rings. Their eyes had both acuity and good sensitivity to light. The midsized rings, combined with larger eyes, allowed dinosaurs to have the best of both worlds.
From their data, researchers were able to determine which of the studied dinosaurs were most likely active during the day and which were more active during the night. They determined that most flying animals were probably diurnal, many carnivores such as velociraptors were nocturnal and herbivores roamed the lands during both day and night.
This discovery challenges the conventional wisdom that early mammals were nocturnal because dinosaurs had already taken the day shift. According to the study, predatory dinosaurs and early mammals were active during the same time of the day.
The results also suggest that predatory dinosaurs may have been warm-blooded — they regulated their internal body temperature with their internal chemistry. This has long been suspected by scientists but until now, paleontologists had lacked evidence. These new results may shed new light on the physiology of dinosaurs.
